The present invention relates generally to telescopes and in particular, to mounts for astronomical telescopes.
There are two basic types of telescope mounts: altazimuth and equatorial, both having two orthogonal axes of rotation. In the altazimuth mount, one axis (altitude) is horizontal and the other (azimuth) vertical. In the equatorial mount, a first (polar) axis is parallel to the earth""s axis (made so by inclining it to the horizontal by an angle equal to the latitude of the viewer) and the second (declination) axis permits adjustment of the angle of inclination. The equatorial mount makes celestial tracking simple: the object is located, the declination axis fixed, and the optical instrument rotated about the polar axis in a direction opposite to, and at a rate equal to the rate of, the earth""s rotation. This is known as driving the telescope in right ascension (so known for the path followed by the light receiving end of the instrument). Although tracking of a celestial object is more difficult with the altazimuth mount, a computer can readily handle the variable drive rates to co-ordinate the complex multiplanar motions, and telescopes with both altazimuth and equatorial mounts are often motor driven.
A fork mounting is used for both altazimuth and equatorial mounts, wherein the telescope is carried between bearings of an axis (altitude or declination) in a fork through which it is swung to gain access to the sky. An altazimuth mounting is a fork mounting with the axis vertical so that the tines have no transverse load. In the equatorial fork mounting, the polar axis is inclined, and the fork itself must be rigid to reduce the bending and twisting deflections of the tines.
Large Cassegrainian telescopes, are often preferred by astronomers and for serious amateur observation by individuals and societies. These telescopes typically have an aperture diameter of about 600 mm or more, with an equatorial or altazimuth fork mount and motor drive. Such telescopes have traditionally been of massive metal construction in order to attain the necessary stiffness to avoid problems associated with deflection. The support frames and foundations for these telescopes have also been correspondingly heavy making them very difficult to relocate.
Lightweight Newtonian telescopes can be readily lifted onto a car trailer and driven to a suitable viewing location. These lightweight instruments however, lack stability and are adversely affected by ground vibration, wind disturbance and operational vibration. As well as having drawbacks for ordinary viewing, this lack of stability reduces their capacity for use with sensitive auxiliary instrumentation, particularly when operating at higher magnifications.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
According to one aspect of the present invention there is provided a mount for supporting a telescope, wherein the mount includes means for containing ballast material.
The mount includes a pivotable frame mounted on a ground-supported frame. The ground-supported frame accommodates a pivotal movement in the pivotable frame, and the pivotable frame includes the ballast containers substantially symmetrically disposed about the axis of the frame.
Preferably, the pivotable frame comprises a fork having a pivot for rotation thereof about a first axis, being the axis of the fork, and the fork defines a second perpendicular axis for rotation of the telescope thereabout. The telescope is supported on bearings between two tines of the fork. Different ground-supported frames are provided to support the yoke in either equatorial or altazimuth alignment.
The ballast containers are liquid tight and adapted to contain flowable ballast material. The ballast allows the most desirable telescope mass to be obtained with any number of conventional or unconventional materials such as, wet or dry sand and or small stones, water, crushed ice and other fluids and semi-fluids and solids.
A conical ballast container is provided at one end of the fork. In the structural yoke joining the two tines of the fork is provided a substantially cylindrical ballast container. The conical container and the substantially cylindrical ballast container are separated by a drive wheel. The fork is supported on a bearing adjacent to the apex of the conical container and on rollers running on the drive wheel. The ballast containers and the wheel may be readily separated for portability.
Before the fork is assembled for use the ballast is loaded thorough closures in the hard shell of the containers.
The containers are made from high modulus lightweight composite materials. This mount, compared to the prior art, offers cost-competitive construction, together with rigidity and low thermal mass, while avoiding the need for massive foundations.
It has been found that the ballast works to improve the stability of the telescope mounting, by both favorably altering the harmonics of the mounting and reducing vibrations of the telescope. The ability to raise the mass of the telescope mount in-situ provides this improved stability by lowering the centre of gravity of the mount. The natural frequency of vibration of the stiff composite fork structure is relatively high, this natural frequency is advantageously lowered by the addition of mass. The presence of the flowable ballast material also serves to dampen vibrations in the mount, dissipating the energy within the ballast material. The high stiffness, lower natural frequency and dampening properties allow a pointing accuracy or tracking ability of the same order as the to be achieved. For example, a pointing and tracking accuracy of a few arcseconds may be readily achieved.